LabJack U3 User Manual
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Contents
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5.2.12 StreamDataAfter starting the stream, the data will be sent as available in the following format. Reads oldedata from buffer. Requires U3 hardware version 1.21.st• SamplesPerPacket: From StreamConfig function.• TimeStamp: Not currently implemented during normal operation, but after auto-recoverythis reports the number of packets missed (1-65535).• PacketCounter: An 8-bit (0-255) counter that is incremented by one for each packet ofdata. Useful to make sure packets are in order and no packets are missing.• Sample#: Stream data is placed in a FIFO (first in first out) buffer, so Sample0 is theoldest data read from the buffer. The analog input reading is returned justified as a 16-bit value. Differential readings are signed, while single-ended readings are unsigned.• Backlog: When streaming, the processor acquires data at precise intervals, andtransfers it to a FIFO buffer until it can be sent to the host. This value represents howmuch data is left in the buffer after this read. The value ranges from 0-255, where 256would equal 100% full.tream mode on the U3 uses a feature called auto-recovery. If the stream buffer fills up, the U3will go into auto-recovery mode. In this mode, the U3 no longer stores new scans in the buffer,but rather new scans are discarded. Data already in the buffer will be sent until the buffer isempty, and every StreamData packet will have errorcode 59. Once the stream buffer has beenemptied, the U3 will start to buffer new scans again. At this point, the next packet returned willhave errorcode 60. This packet will have 1 dummy scan where each sample is 0xFFFF, andthis scan separates new data from any pre auto-recovery data. Also, the TimeStampparameter in this packet contains the number of scans that were discarded, allowing correcttime to be calculated. The dummy scan is included in the TimeStamp value.Response:Byte0 Checksum81 0xF92 4 + SamplesPerPacket3 0xC04 Checksum16 (LSB)5 Checksum16 (MSB)6-9 TimeStamp10 PacketCounter11 Errorcode12-13 Sample062 (max) Backlog63 (max) 0x00S102 |
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